Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’-Thimble Cactus

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 7-8-18, #473-13.

Thimble Cactus

Mammillaria vetula subsp. gracilis 

‘Arizona Snowcap’

mam-mil-AR-ee-uh  VET-uh-luh  GRASS-il-is

Syn. of:

Mammillaria vetula

Commonly sold as:

Mammillaria gracilis var. fragilis

mam-mil-AR-ee-uh  GRASS-il-is  FRAJ-ih-liss

Other synonyms of Mammillaria vetula from Plats of the World Online (24) (List last updated on 12-21-20): Cactus gracilis (Pfeiff.) Kuntze, Cactus pulchellus (Salm-Dyck) Kuntze, Cactus regius (C.Ehrenb.) Kuntze, Cactus vetulus (Mart.) Kuntze, Chilita fragilis (Salm-Dyck ex K.Brandegee) Orcutt, Chilita vetula (Mart.) Orcutt, Escobariopsis gracilis (Pfeiff.) Doweld, Escobariopsis vetula (Mart.) Doweld, Krainzia gracilis (Pfeiff.) Doweld, Mammillaria fragilis Salm-Dyck ex K.Brandegee, Mammillaria gracilis Pfeiff., Mammillaria gracilis var. fragilis A.Berger, Mammillaria gracilis var. pulchella (Salm-Dyck) Salm-Dyck, Mammillaria gracilis f. pulchella (Salm-Dyck) Schelle, Mammillaria grandiflora Salm-Dyck, Mammillaria kuentziana P.Fearn & B.Fearn, Mammillaria magneticola J.Meyrán, Mammillaria pulchella Salm-Dyck, Mammillaria regia C.Ehrenb., Mammillaria vetula subsp. gracilis (Pfeiff.) D.R.Hunt, Mammillaria vetula subsp. lacostei Plein & Heinr.Weber, Mammillaria vetula subsp. magneticola (J.Meyrán) U.Guzmán, Neomammillaria fragilis (Salm-Dyck ex K.Brandegee) Britton & Rose, Neomammillaria vetula (Mart.) Britton & Rose

***Although there are differences, Plants of the World Online by Kew lists Mammillaria vetula subsp. gracilis as a synonym of Mammillaria vetula. According to descriptions, Mammillaria vetula has 1-2 central spines and 25 radial spines where Mammillaria vetula subsp. gracilis has NO central spines. My plants have no central spines so I am continuing to acknowledge the subspecies. It’s my site and I can call it what I choose as long as the name was validly published, which it was in 1997. 🙂 

Mammillaria vetula Mart. is now considered the correct and accepted scientific name. It was named and described as such by Carl (Karl) Friedrich Philipp von Martius in Nova Acta Physico in 1832.

Mammillaria vetula subsp. gracilis (Pfeiff.) D.R.Hunt is now considered a synonym of Mammillaria vetula. This subspscies was named and described as such by David Richard Hunt in Mammillaria Postscripts in 1997. It was first named Mammillaria gracilis Pfeiff. by Ludwig Karl Georg Pfeiffer in Gartenzeitung in 1838.

Mammillaria gracilis var. fragilis A.Berger was named and described by Alwin Berger in Kakteen in 1929. This name is what the industry is commonly using…

The genus, Mammillaria Haw., was named and described by Adrian Hardy Haworth in Synopsis Plantarum Succulentarum in 1812.

Plants of the World Online by Kew lists 164 accepted species in the Mammillaria genus (as of when I am updating this page on 12-21-20). It is a member of the plant family Cactaceae with 144 genera. That number is likely to change as updates are made.


Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 7-8-18, #473-14.

I brought this cactus home from Lowe’s on July 8, 2018. The label said it is a Mammillaria gracilis fragilis monstrose. I thought it was especially neat because it was so white.

The label says:

“Mammillaria gracilis v. fragilis monstrose is a special monstrose cultivar of the charming miniature Mammillaria gracilis fragilis. Clusters prolifically to form mats. Satiny creamy yellow flowers in the late winter. Protect from frost to prevent scarring. Provide bright light; hardy to 20F; to 4” tall. Water thoroughly when soil is dry.

The sides of the 11 oz. (3 1/2″ tall x 3 1/2″ diameter) pot was bulging. The cluster of plants measured 2″ tall x 5″ wide and was hanging over the sides of the pot.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 7-8-18, #473-15.

I had to do a little research about this plant before I published information about it and I found out it was likely the cultivar ‘Arizona Snowcap’. The cultivar was created “in captivity” and it may even be a hybrid. The species, Mammillaria vetula and subspecies Mammillaria vetula subsp. gracilis are native in the states of Hidalgo, Guanajuato, and Querétaro in Mexico where they are found in pine forests at high altitudes. 

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 7-8-18, #473-16.

Mammillaria vetula and the subspecies are small, freely clustering plants that can grow 4-5″ tall x about 1 1/2″ in diameter… Not sure how long that takes because none of mine ever grew that big. Supposedly, the offsets of the species are not as bad about falling off as the subspecies.

Their tubercles are round, bluntly conical and the areoles have a small tuft of wool. The axils between the tubercles on the subspecies and cultivar are bare while the species may be slightly wooly and bristly (hairs).

The areoles on top of the tubercles of the species produce 25 or so (up to 50 on mature specimens) white radial spines while the subspecies have 11-16. The radial spines on ‘Arizona Snowcap’ are shorter, thicker, and very dense. The species generally have 1-2 reddish-brown central spines that are longer than the radials. The subspecies and cultivar “usually” have no central spines.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 7-8-18, #473-17.

Llifle (Encyclopedia of Living Forms) says “Mammillaria ‘Arizona Snowcap’ is a monstrous form of Mammillaria vetula subsp. gracilis which is characterized by densely packed separate clusters of spines. It looks so different from the wild species that it isn’t easy to realize that they are related. This cultivar offsets generously from sides and upper part of the plant, which gives it a snowball appearance. A mature group can reach 10-12 cm in diameter and 6-8 (10) cm in height.”

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 7-29-18, #487-70

I put the cluster of plants in a larger pot so it could have more room…

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 8-18-18, #498-5.

Mammillaria vetula subsp. gracilis ‘Arizona Snowcap’ look their best if grown in full sun, so I put it on the back deck with most of the other cactus.

Mammillaria vetula (subsp. gracilis) on 8-26-18, #499-28.

 They did very well over the summer in full sun and I didn’t notice any sunburn.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ at 1 5/8″ tall x 5 1/8″ wide on 10-10-18, #519-54.

I had to move the potted plants inside for the winter on October 10 (2018) because the forecast was calling for an “F” in a few days and the nighttime temperatures were getting cooler. I usually measure the cactus and succulents when I bring them inside. This cluster of plants measured 1 5/8″ tall x 5 1/2″ wide.

It is recommended that they watered sparingly during the summer and barely it at all during the winter months. I usually go over my cactus and succulents at the same time as my other potted plants, but I go over them quickly. 

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-29-18, #534-28.

November 29 was a nice spring-like day, so I took the cactus to the back porch for a photoshoot. I was working on a post to show the difference between the cactus in my collection.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-29-18, #534-29.

I had a Mammillaria vetula subsp. gracilis before that was much different. When I first brought this plant home none of the offsets were as thickly covered as a few are now but I still knew it was different than the previous one. In fact, there was one next to it at Lowe’s when I found this one like I had before. Strange only a few offsets spines are thicker and the others aren’t. It is going to be an interesting plant to watch.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ close-up on 12-1-18, #535-21.

The species, Mammillaria vetula, has 1-2 central spines and at least 25 radial spines. The subspecies often lack the central spines and only have 11-16 radial spines. The plant I had before also had much longer spines. Its flowers are also shorter. I noticed the areoles on the top have a small tuft of wool but not so much on the lower parts.


Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 5-25-19, 576-53.

Once evening temperatures warmed up I moved the potted plants back outside for the summer. I moved the cactus to the back porch where they could receive full sun. Unfortunately, many offsets died over the winter, including the ones that were more white. Maybe the monstrous mutation makes them more “fragilis”.

I was fairly busy during the summer so I didn’t take many photos. All the plants did very well despite a little neglect.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 10-11-19, #639-74.

I had to bring the potted plants inside on October 11 because an “F” was in the forecast. I always take photos of the plants as I bring them inside and measure the cactus and some of the succulents. Several of the “whiter” offsets had died and one had a bud…

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 10-13-19, #641-3.

Then another…

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-2-19, #646-7.

November 2 was a nice spring-like day so I took several cactus that were flowering to the front porch for a photoshoot.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-16-19, #651-2.

On the 16th I decided it was high time I worked on the Mammillaria vetula subsp. gracilis ‘Arizona Snowcap’. I had already re-potted several other cactus and succulents. Some just needed their soil changed while others needed bigger pots. I used about 50/50 Miracle Grow Potting Soil and pumice for the mix. There are many recipes online for cactus and succulents, but I prefer something simple. I had used a mixture of 2 parts potting soil with 1 part chicken grit and 1 part perlite for many years then read where succulent enthusiasts prefer pumice. SO, I have been trying that since the fall of 2018 with favorable results. I repot any time of the year as necessary, but I have found Fall is a great time. After a summer of regular watering, the potting mixture can become kind of hard when it is decreased. Repotting in the Fall gives the plants nice and loose soil for the winter.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-16-19, #651-3.

The largest cluster seemed to be pretty well intact.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-16-19, #651-4.

After removing the clump from the pot I had to remove the dead…

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ repotted on 11-16-19, #651-5.

Then I kind of centered the live plants around the larger cluster.

Dead Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-16-19, #651-6.

This is part of the dead plants. I had discarded a few earlier in the summer. Hopefully, the rest will do OK over the winter.


Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ at 1 1/2″ tall on 10-15-20, #747-80.

I had to bring the potted plants inside for the winter on October 15 (2020) because an “F” was in the forecast. As always, I took photographs and measurements. The Mammillaria ‘Arizona Snowcap’ did very well over the summer and FINALLY, some of the plants in the cluster are more white. The tallest plant in the group measured 1 1/2″ tall on October 15.

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 10-15-20, #747-81.

As you can see in the above photo, some of the plant’s spines seem thicker. I was waiting for this… One of the largest plants in the group has a circle of buds. 🙂

Mammillaria vetula (subsp. gracilis) ‘Arizona Snowcap’ on 11-6-20, #755-5.

LOOKING GOOD on November 6. Interesting how such a small plant can have a circle of flowers.

Family: Cactaceae
Origin: Nursery origin. Species from Mexico
Zones: USDA Zones 10a-11 (30 to 40° F)
Size: Hmmm…
*Light: Sun to part shade. Looks best when in full sun but needs to be introduced gradually.
**Soil: Very well-draining soil. Potting soil with additional perlite and grit or pumice.
***Water: Water sparingly during the summer and barely in the winter.

*During the summer, I keep most of my cactus on the back deck where they receive full sun. During the winter most cactus aren’t picky about the light because they are basically dormant. For several winters, mine were in front of the east-facing sliding door in the dining room so they didn’t get much light but they did great. I built a new shelf for the bedroom so now they are in front of a west-facing window. Most of the succulents are on a shelf in a south-facing window in a cool bedroom but a few are in my bedroom.

**When it comes to potting soil, finding the “sweet spot” is not exactly that easy when materials are limited. Cactus and succulent enthusiasts (and experts) do not recommend using peat-based commercial mixes but what choice is there for most of us. They say to use a loam-based mix… Hmmm… Our soil is loam, so do I just use dirt? Well, no because “dirt” is heavy and you need a “light” material. There is A LOT of cactus and succulent recipes online and some get pretty elaborate. Many say to use sand as an ingredient, but if you do that, it needs to be very coarse, like builders sand, because “ordinary” sand, like for sandboxes, is too fine and it clogs up the air space between the coarser ingredients. For MANY years I used 2 parts Miracle Grow or Schultz Potting amended with an additional 1 part of perlite and 1 part chicken grit. Schultz doesn’t seem to have as many large pieces of bark. Cactus and succulent enthusiasts recommended using pumice instead of perlite and grit so I checked it out… The “guy” at General Pumice (online) recommended using a 50/50 mix of potting soil and pumice. General Pumice has 3 different sizes to choose from depending on the size of the pot. SO, in 2018 I bought a bag of 1/8″ and mixed it 50/50 with Miracle Grow Potting Soil. I liked it pretty well. Then in 2020, since most of the cactus were in larger pots, I ordered the 1/4″ size. Pumice has a lot of benefits over perlite and has nutrients that are added to the soil when watering. Pumice is also heavier so it stays mixed in the soil instead of “floating” to the top. Still, there is the issue of the mix getting very hard once you stop watering the plants during the winter when you stop watering. I think this is because of the peat in the potting soil… SO, instead of re-potting the cactus and succulents in the spring, I started doing it during the fall and winter so their soil would be loose. Since you don’t water as frequently during the winter if at all, the timed-release fertilizer does not activate. I have not tried coir, but I am looking into it… 

I think a lot of growing tips online are written by people who never grew succulents and cactus. They just copy from one website and paste it to theirs. You have to sort of mimic the soil where species grow in their native habitat. For that, you almost have to go see for yourself… Typically, they grow in fairly rocky soil.

***I water my cactus and succulents on a regular basis during the summer but barely ever in the winter (maybe a little in January) until close to time to take them back outside. 

You can read my Cactus Talk & Update and Cactus & Succulent Tips to get my opinion about growing cactus and succulents.

When you bring your new plants home from the store, you need to check their roots and the soil to see if they are wet. If so, you may want to re-pot it right away. It is advisable to re-pot them in a better potting soil more suitable for cactus and succulents.



There isn’t much online about this cultivar yet, but maybe someday there will be more.

I hope you enjoyed this page and maybe found it useful. If you have any comments, questions or suggestions, I would like to hear from you. Please click on “like” if you visited this page. It helps us bloggers stay motivated. 🙂 You can check out the links below for further reading. The links take you directly to the genus and species of this plant.


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